I am just entering the surplus firearms arena, and am interesting in how pitting in the bore effects accuracy and function. I know what a "mirror" bore looks like, but how does one differentiate between a "frosted," "pitted," and "sewer pipe" barrel?

I was inspecting an Egyptian FN49 today and saw that the last few inches of the barrel were fairly corroded. Is the going to result in a drastic loss in accuracy?

Frosted -- the bore looks similar in quality to "mirror" in respect
to condition except that it is not shiny. Has a dull appearance to it.
This is invariably due to lack of timely cleaning after the rifle has
been fired with corrosive primed ammunition. Bore has kind of a
sand blasted appearance.

Pitted -- this is an expansion of the frosting condition. The integrity
of the surface has now progressed to an eroded state. You will observe
"spots" in the bore that will not clean out.

Sewer -- bad state of pitting.

The problem with all of these bore conditions is that metal will strip
off of the bullet jacket as it traverses the bore. This will copper foul
the bore and accuracy will be impaired eventually. Cleaning the bore
is a (much) more tedious job than with a mirror condition bore.

Some rifles with poor condition bores due turn in respectable accuracy,
but this is more of an anomaly. Be wise. Avoid rifles with these kinds
of bore conditions if all possible.

However, all that being said, I have seen many barrels that were pited that shot minute of angle. Don't throw out the baby with the bath water. Shoot it , see how it shoots. I had an 03 Springfield that had a sewer pipe for a barrel, shot like a dream. Sold it to a friend years ago, he unts with it and bags a deer every year.

Mosin-Nagants are the worst....corrosive old 7.62 ammo and "former owners" (ie, soviet infantry conscripts) whose life-expectancies were much shorter than the rifles - all make for about 40 million surplus rifles with horribly neglected bores. I have owned a couple of them and all have frosty barrels. They shoot straight still. Sometimes it comes clean with shooting, sometimes it doesnt. Just make it as clean as it will get and shoot it

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